1. Field of the Invention
The present invention relates to an electronic fuel injection control method and apparatus for supplying fuel to an internal-combustion engine (hereinafter, referred to as an “engine” as appropriate), and more particularly, to a fuel injection control method and apparatus for accurately supplying a fuel injection amount required from the engine side while eliminating effects due to variations in coil resistance of a fuel injection solenoid generated by variations in power supply voltage and temperature, and others.
2. Description of Related Art
It is extremely an important factor that affects the performance of the entire engine to supply fuel to the engine of a vehicle including a two-wheeled vehicle at suitable timing corresponding to a fuel injection amount required from the engine side that varies every instance. Therefore, an electronic fuel injection apparatus has been used that electronically controls the fuel injection to the engine using a microcomputer.
FIG. 20 illustrates a specific example of a control circuit of such an electronic fuel injection apparatus. In this example, a fuel injection amount per unit time injected from the fuel injection apparatus varies due to variations in power supply voltage (battery voltage), in view of which, the fuel injection time is adjusted using a level of the power supply voltage. In other words, the power supply voltage VB applied to a power supply terminal 11 is input to a microcomputer 13 of ECU (Electronic Control Unit) via a power supply voltage input circuit 12. When the power supply voltage VB is low, the microcomputer 13 outputs a driving pulse with a longer ON time of a FET 14 to a FET driving circuit 15 so as to adjust the driving time (fuel injection time) of a fuel injection solenoid 16 to be longer. Meanwhile, when the power supply voltage VB is high, the microcomputer 13 outputs a driving pulse with a shorter ON time of the FET 14 to the FET driving circuit 15 so as to adjust the driving time of the fuel injection solenoid 16 to be shorter. In this way, the fuel injection amount is controlled so that a required proper amount of fuel is supplied without being affected by variations in power supply voltage. An example of the fuel injection control method is disclosed in Patent Document 1 for thus adjusting a fuel injection amount by detecting a level of the battery voltage.
FIG. 21 shows an example of another well-known technique of control circuit for an electronic fuel injection apparatus. In the circuit, the power supply voltage VB applied to the power supply terminal 11 is detected in a power supply voltage detecting circuit 21, while a coil current of a fuel injection solenoid is detected using resistance 22 and current detecting circuit 23 added for current detection. Thus, the coil current is controlled not to vary due to variations in power supply voltage VB using the microcomputer 13 and a constant-current driving circuit 20.
Patent Document 2 describes an example of such an injector driving apparatus which detects a driving current flowing through an injector (fuel injection apparatus), and based on a detected value of the injector driving current, corrects a delay time in valve opening time of the injector.
Further, there is known a driving control apparatus of a fuel injection valve for an engine where a fuel temperature is detected in relation to a temperature of a fuel injection electromagnetic coil, a correction pulse width is set to compensate for an operation delay time in the fuel injection valve based on the fuel temperature and battery voltage, and a final injection pulse width is obtained by adding the correction pulse width to an effective injection pulse width corresponding to a fuel amount to supply to the engine (for example, Patent Document 3).
[Patent Document 1] Japanese Laid-Open Patent Publication No. S58-28537
[Patent Document 2] Japanese Laid-Open Patent Publication No. 2002-4921
[Patent Document 3] Japanese Laid-Open Patent Publication No. H08-4575
However, for example, in the control method as described in Patent Document 1 and FIG. 20 where the fuel injection time is corrected based on a level of the power supply voltage, when the temperature of the coil that composes the solenoid 16 increases, since the resistance of the coil varies and the coil current varies even in the same power supply voltage VB, it is difficult to supply a required fuel injection amount properly. This is because a fuel injection amount per unit time of the solenoid 16 varies with the coil current value.
Therefore, the fuel injection solenoid is driven with a constant current, or a delay in valve opening time of the injector is compensated based on a detected value of an injector driving current (coil current) as disclosed in Patent Document 2. However, the solenoid is affected by the temperature in its operation characteristics including the operation starting time after the voltage is supplied, and therefore, cannot respond to a fuel injection amount required from the engine side properly. Further, since the driving control circuit and the software processing is complicated, it is difficult to implement size reduction and cost reduction in the entire fuel injection apparatus.
Further, in the driving control apparatus of a fuel injection valve for an engine as disclosed in Patent Document 3, the temperature of fuel is measured to indirectly detect the temperature of an electromagnetic coil that is a factor for causing the operation characteristics to vary. However, the temperature of the electromagnetic coil does not agree with the temperature of fuel always, and the detecting means for detecting the temperature of fuel should be placed inside the fuel tank together with the driving control apparatus of a fuel injection valve for an engine, resulting in a problem that decreases a fuel storage capacity of the fuel tank corresponding to such placement.